This invention relates to an image intensifier tube and more particularly to electromagnetic interference (EMI) protected image intensifier.
Image intensifier tubes multiply the amount of incident light they receive and thus provide an increase in light output which can be supplied either to a camera or directly to the eyes of a viewer. These devices are particularly useful for providing images from dark regions and have both industrial and military application. For example, these devices are used for enhancing the night vision of aviators, for photographing astronomical bodies and for providing night vision to sufferers of retinitis pigmentosa (night blindness).
Modern image intensifier tubes include three main components, namely a photocathode, a phosphor screen (anode) and a microchannel plate (MCP) positioned intermediate the photocathode and anode. The photocathode is extremely sensitive to low-radiation levels of infrared light in the 580-900 nm (red) spectral range. The MCP is a thin glass plate having an array of microscopic holes through it. Each hole is capable of acting as a channel-type secondary emission electron multiplier. When the microchannel plate is placed in the plane of an electron image in an intensifier tube, one can achieve a gain of up to several thousand. Since each channel in a micro-channel plate operates nearly independently of all the others, a bright point source of light will saturate a few channels but will not spread out over adjacent areas. This characteristic of "local saturation" makes these tubes more immune to blooming at bright areas.
When the image intensifier without EMI protection is operated in an electromagnetic field, such as in the vicinity of an operating high power radio or radar transmitter, the image intensifier will suffer degradation in performance. The output will either go black or very bright or some point in between, depending on the design of the power supply. Increased brightness is distracting and in extreme situations will cause the user to lose all contrast, producing a blank viewing screen.
It is therefore an object of the present invention to provide an image intensifier tube having protection from electromagnetic interference.
It is an additional object of the invention to provide a method of making such a tube in a highly economical and efficient manner.
These objects and others which will become apparent hereinafter are accomplished by the present invention which provides an image intensifier device including means for amplifying an image formed of photons of light; power supply means for operating the amplifying means; and means for protecting the amplifying means and the power supply means for electromagnetic interference.
The present invention also provides a method for protecting an image intensifier tube from electromagentic interference by directing electromagnetic interference from a power input location to ground, and shielding the tube by applying a conductive coating to reflect the interference away from the tube.